Planing boats operating in rough water may experience significant vertical shocks when the boat and wave impact one another. The most powerful shocks occur after a boat has become airborne flying off the crest of a wave, when the boat lands onto a wave face with its keel substantially parallel to the wave surface. Shock impulses on the order of 50 Gs with pulse durations in excess of 40 milliseconds are not uncommon, and suck shock is more than enough to cause serious injury. Documented injuries include sprains to the back, neck, hip, knee, and shoulder, kidney damage, and broken ribs and limbs.
Typically, naval architects have attempted to reduce this shock by deepening and narrowing the hull, and pointing the bow. These deep-vee hulls impact the water more gradually and with less peak acceleration than shallower, flatter hulls. But deep-vee hulls require deeper water for safe navigation may have roll stability issues, and generally require more fuel for a given speed than shallow-vee hulls. Moreover, they cannot unquestionably limit the acceleration on the Payload in all cases of boat-water impact.
Boat operators typically attempt to reduce shock by either slowing down considerably in rough water, or slowing down somewhat while attempting to steer and throttle around the biggest waves while avoiding becoming airborne. The drawback of these approaches is the speed reduction. Military and law-enforcement boats often cannot slow too much without risking mission failure. Offshore power boats cannot slow too much without risking the race.
A number of hardware devices have been developed and are in use, including several that have been patented. All have drawbacks. Perhaps the most serious drawback of previous approaches is that they cannot protect the Payload if the incident shock peak or its rate of rise is too large. Many of these devices work reasonably well provided the peak shock amplitude is fairly low, for example, shock peak under 10 G's with jerk under 100 G's per second. But the performance of these same devices degrades as the rate of rise and/or peak amplitude of the acceleration increases. Faster boat speeds and rougher seas create sharper, more powerful shocks, with peaks on the order of 50 G's and jerk on the order of 1,000 G's per second. Previous approached are generally based on viscous dampers and springs. A viscous damper's force is a function of the relative velocity of its endpoints. Even if actively controlled, a viscous damper transmits forces to the Payload which depend on the peak load and loading rate of the shock pulse.
A problem related to protection from boat shock is protection from explosive shock. Explosive devices generate accelerations on the order of thousands of G's with jerk on the order of tens of millions of G's per second. Explosions have such short pulse durations, as small as a fraction of a millisecond, that an active protection system would require an extremely high sampling rate, some very rapid processing algorithms to discriminate between noise and an actual explosion, and very rapid actuators to effect protection of the Payload, making an active protection system very expensive, if it could be made at all. Current approaches using passive viscous damping systems would either break or dump fluid out their relief valve under such extreme forces. Traditional approaches to protecting against shock differ somewhat depending, upon the nature of the Payload. If the Payload consists of equipment, the traditional approaches have been to either harden it or mount it on resilient mounts. Hardening generally results in increased weight and volume, and often impacts accessibility or maintenance and convective cooling. Resilient mounting often exacts volume penalty in order to accommodate sway and surge of the equipment during shock. In cases where the Payload is personnel, there have also been two similar traditional approaches. The first is to brace for shock, generally involving bending the legs and holding onto handrails while tensing the muscles. The other approach has been some type of resilient interface such as padded seating or heavy sponge rubber deck covering on a ship traversing a suspected minefield. No systematic, engineered approach which can unequivocally protect a Payload from explosive shock has been developed. Another drawback of many previous approaches is an inability to adjust to the weights of various Payloads. These devices are either overly stiff or overly-soft depending upon the Payload-mass. Overly stiff devices obviously transmit too much force to the Payload. But overly soft devices may also be inadequate in that they expend all available relative displacement between Payload and vehicle without absorbing all the shock energy. The Payload then bottoms out, spiking the acceleration. Even if the Payload does not bottom out, an overly soft interface takes up more volume than required, impacting its usefulness, particularly in high-performance vehicles. A further drawback of previous devices is a slow reset time. If the device cannot restore the Payload to its original position before the next shock hits, then the next shock may cause it to bottom out.
The purpose of the present invention is to protect the Payload (personnel and sensitive equipment) firm shock. It does so by limiting the force transmitted to the Payload to a low, user-adjustable value, regardless of the peak amplitude or rise rate of the imposed shock on the vehicle or structure. Another purpose of the present invention is to provide adjustment of the force transmitted to the Payload from the vehicle or structure to accommodate the masses of various Payloads without being overly stiff or bottoming out. Anther purpose of the present invention is to have a quick reset time so that it can be fully recovered in time for each subsequent shock events. BRIEF DESCRIPTION OF THE INVENTION In accordance with the foregoing purposes and other purposes and intents, the invention is based upon three, required principles and one optional principle. The first principle is limiting the acceleration upon the Payload regardless of the peak shock imposed upon the vehicle.
The second principle is that the displacement required to dissipate the shock energy be minimized. The third principle is adjustability to accommodate range of Payload masses. The fourth principle is optional and is the ability to react to an impending shock by repositioning the Payload to gain more displacement over which to dissipate the shock energy. A number of useful ways to implement the above principles are conceived. Various seating systems, equipment foundations, cockpit enclosures, platforms, and even entire chambers can be isolated from their surroundings by the present invention. The invention is generically comprised of four required assemblies, plus one optional assembly.
(1) The Frame Assembly (FA) mounts directly to the vehicle. It provides Structural support to the other major assemblies, constraining their movement to within acceptable limits, and enabling them to function properly.
(2) The Payload Interface Assembly (PIA) directly interfaces with the Payload. It directly supports and restrains the Payload. It provides monitoring and control capabilities for the invention.
(3) The Suspension Assembly (SA) supports the PIA. During a shock, the SA works with the EDA to allow the PIA to move just enough to avoid exceeding the acceleration limit on the Payload, and then recovers the PIA.
(4) The Energy Dissipating Assembly (EDA) dissipates the shock energy.
(5) The optional Shock Anticipating Assembly (SAA) is a reactive assembly which repositions the PIA just prior to shock so that more displacement is available to absorb or dissipate the shock. According to one aspect of the invention, a limiting interface for supporting a payload relative to a structure includes a frame assembly attached to the structure, a payload interface assembly for receiving the payload, a suspension between assembly disposed between the frame assembly and the payload interface assembly, and an energy dissipating, assembly disposed between the frame assembly and the payload interface assembly. The energy dissipating assembly is adapted to dissipate energy transmitted to the structure, so as to limit a parameter of interest transmitted to the payload. Depending on the particular application, in various embodiments, the parameter of interest can be displacement, time integrals of displacement including velocity, acceleration and jerk, as well as vibration, force, energy, and shock. Based on an event that causes an input to the structure, the limiting interface can be configured to attenuate the energy, so ask to transmit to the payload a predetermined maximum parameter of interest in a predetermined manner. For example, in one embodiment, a force displacement profile of the payload interface assembly is substantially linear. Alternatively or additionally, in another embodiment, the force-displacement profile of the payload interface assembly is substantially constant. In yet another embodiment, the force displacement profile of the payload interface assembly is substantially a square wave. The limiting interface may optionally include an anticipating assembly disposed between the frame assembly and the payload interface assembly that repositions the payload interface assembly relative to the structure from a neutral position in anticipation of an event. In one such embodiment, the anticipating assembly increases a range of travel of the payload interface assembly relative to the structure in anticipation of an event. In various embodiments of the invention, the suspension assembly permits relative movement between the payload interface assembly and the structure in a first direction only, when acceleration or other parameter of interest transmitted to the payload is about to exceed a predetermined value. In still other embodiments of the invention, the suspension assembly permits relative movement between the payload interface assembly and the structure in a first direction only, for as long as acceleration or other parameter of interest transmitted to the payload is about to exceed a predetermined value. According to one embodiment, the limiting interface and the energy dissipating assembly are capable of accommodating a plurality of events. The limiting interface may be reset automatically or, alternatively, manually. In various embodiments of the resetting type, after at least one event, the payload interface assembly is returned to a neutral position by the suspension assembly. In other embodiments, the energy dissipating assembly is capable of accommodating a single event, and can be rebuilt or refurbished to restore functionality.
In various embodiments, whether multiple event, single event, resettable or refurbishable, the energy dissipating assembly may be configured to convert kinetic energy transmitted to the structure at least partially into thermal energy. In some embodiments, the energy dissipating assembly may be configured to deform an element, elastically and, optionally, plastically. The energy dissipating assembly may be a friction brake, of any of a variety of configurations. The limiting interface may advantageously be adjustable, to accommodate payloads of various configurations and mass, including equipment and personnel. In those instances where the payload is a person, the payload interface assembly may be a platform, bench, seat, or any suitable supporting structure for a person. Similarly, the structure may be any of a variety of structures, including aeronautic-based, land-based, or water-based vehicles.
According to another aspect of the invention, a method for supporting a payload relative to a structure includes, in one embodiment, the steps of providing a limiting interface attached to the structure and adapted to receive the payload and dissipating energy transmitted to the structure, so as to limit a parameter of interest transmitted to the payload. In one embodiment, the limiting interface does so by converting at least a portion of kinetic energy transmitted to the structure to substantially a square wave force-displacement profile transmitted to the payload. Alternatively or additionally, a magnitude of the force-displacement profile may be substantially constant. In general, the magnitude of the square wave force-displacement profile is less than a predetermined value.